The subject matter disclosed herein relates to the art of electrical equipment and, more particularly, to an electrical equipment assembly and a method of calibrating an electrical equipment assembly.
Electrical power protection equipment systems typically include a power transformer, a current transformer or Rogowski, a command trip unit and an interruption device (circuit breaker). Often times a meter is added to the power protection equipment to aid application engineers in facility management. In order to ensure proper metering, each component of the power protection equipment is calibrated and a measurement tolerance determined. The components are then assembled and the protection equipment is installed into a facility. However, while many of the individual components are individually calibrated, overall measurement accuracy is a function of the tolerances of each component. With this arrangement, eliminating measurement error is very difficult.
In order to address this issue, manufactures hold calibration until final assembly. Once final assembly is complete, a known current is injected into the electrical system. An output of the system is requested from the command trip unit and is compared with the known current. Any difference between the known current and the measured current determines an offset value that is used to calibrate the protection equipment. A similar off-set value is also calculated for voltage. While effective at minimizing measurement error, all calibration must be done at the time of final assembly. As such, any in field replacement of protection equipment components will introduce errors into the system and accuracy will be lost.